Normal size clothed human
When you add Collision in the physics properties this includes settings for interaction with Cloth and Soft Body - the Inner and Outer values.



These are typically in Blender Units (or whatever units you have your scene set to) so 0.02 Outer would relate to 2cm if 1BU = 1m. You therefore may need to review your collision settings for the scale. Also, always ensure you Apply Scale on your model and cloth objects.